Solenoid control valves are well-known and are suitable for a wide variety of applications. Solenoid control valves typically have a coil of wire surrounding an armature and an end cap or plug. The armature and cap are made of a ferro-magnetic material, and are coaxially arranged with an air gap therebetween. A valve member extends from the armature, and when the coils are energized, the armature, and hence the valve member, are moved due to magnetic flux forces through the air gap. For proportional solenoid control valves, the movement of the valve member is proportional to the input current or voltage on the solenoid coils.
One type of proportional solenoid control valve is a pilot-operated valve, that is, a valve which has a pilot valve member and a main valve member. The solenoid in such a valve controls the position of the armature to move either the main valve member to an actuated position, or the pilot valve to an actuated position to thereby allow movement of the main valve member. Pilot-operated valves are most typically used in high pressure situations where smooth control of the flow is necessary.
It is believed that pilot-operated proportional control valves can have certain limitations which make them undesirable in certain circumstances. In particular, these valves can have a complicated structure, which can make them costly and time-consuming to manufacture and assemble. Still others can require additional damping to stabilize the valve or to provide a smooth threshold control. Further, others do not maintain consistent performance at varying loads or pressures. Still others, like the valve shown in Kramer, U.S. Pat. No. 4,799,645, have a nose inlet and side outlet which make it difficult (or impossible) to use in place of many existing on/off (i.e., non-proportional) valves in the marketplace. This can prevent the on/off type of valves from being easily upgraded to a proportional type of valve.
Thus, it is believed there is a demand in the industry for a pilot-operated proportional control valve which has a simple structure, requires no additional damping for stable operation, has smooth threshold control, and achieves consistent performance at varying loads and pressure. Finally, it is believed there is a demand in the industry for a proportional control valve which can easily replace conventional on/off valves existing in the market, such that the on/off valves can be easily upgraded to the proportional valve simply by removing the existing on/off valve and replacing it with the proportional valve.